Historically, the fireplace was an important functional element of early houses in Europe and North America, serving as the principal source of heat for the room in which it was located. The conventional fireplace heats the ambient principally by radiative heating and therefore approximately 85% of the heat value of the fuel burned therein is wasted in the form of the combustion gases which are conducted out of the firebox before their heat content can be usefully extracted. The 20th century has seen the fireplace, as a functional heating element, supplanted by more efficient centralized heating systems burning fuel such as natural gas, oil, coal or electricity. Although the operational fireplace is retained in many homes being built today, it serves principally as an ornament, being put to use only on special occasions.
However, with the advent of a world wide scarcity in the fuels used in domestic, centralized heating systems, interest has been rekindled in making use of the erstwhile ornamental fireplace, as a functional element in the heating of the home. The importance of making the conventional domestic fireplace an efficient heating plant with a minimum investment of money and labor in the conversion thereof, can be appreciated.
Since the fireplace is so venerable a part of the household in the western hemisphere, work has been done in the prior art directed to the improvement in the efficiency thereof. For example, cumbersom superstructures, insertable into the firebox, have been developed which employ air convection principles to circulate air about the firebox and back into the ambient. These large structures are characterized by their difficulty of installation, their suitability for only a particular dimension of fireplace, their inefficient extraction of heat from combustion gases, and their constriction of the free flow of the gases into the flu. Access to the damper and throat of the fireplace for maintenance and cleaning is difficult. Other approaches to improving the heat efficiency of the conventional fireplace include the use of a small, roll-about heat exchanger assembly which can be rolled into the firebox and attached to a source of forced air. This type of heat exchanger apparatus fails to optimally extract heat from the combustion gases since it does not take advantage of the substantial amount of heat conducted and radiated rearwardly of the fire and the assembly lacks adjustment features to permit it to conform to the contours of the firebox, thereby making maximum use of the heat developed therein. Still other approaches have employed the use of a duct beneath the grating within the firebox for heating forced air conducted therethrough, by radiation. This type of apparatus is even more inefficient than those previously discussed, making no use of the substantial heat content of the combustion gases flowing up the throat of the fireplace.